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Mozilla released a Firefox Nightly test build with vertical tabs - gHacks Tech News
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Linux is a family of open source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991 by Linus Torvalds. Linux is typically packaged in a Linux distribution (or distro for short).
Distributions include the Linux kernel and supporting system software and libraries, many of which are provided by the GNU Project. Many Linux distributions use the word "Linux" in their name, but the Free Software Foundation uses the name GNU/Linux to emphasize the importance of GNU software, causing some controversy.
Community icon by Alpár-Etele Méder, licensed under CC BY 3.0
I just spent 3 days learning a basic level of css and messing around in my userchrome and NOW they decide to add it...
Your CSS knowledge is still useful to customise other areas of Firefox UI.
Useful ... and mandatory!